The present invention relates to a machine for preparing and laying a bituminous carpet, which may have particular elastic characteristics, for closing microtrenches, the latter having been excavated in the road surface for laying infrastructures such as electric or optical-fiber cables.
The machine according to the present invention can prepare the bitumen for laying, and can lay a bituminous product, which may have particular elastic characteristics, for closing microtrenches less than 30 cm wide, e.g. approx. 10 cm or 5 cm wide.
Bitumen laying machines are known which can lay a bituminous carpet wider than 50 cm for road resurfacing purposes.
Such machines can only lay a bitumen carpet along the path carried out by the machine itself, in particular on the layout traced by the machine itself.
Such machines comprise an accommodating tank for bitumen, which is normally in crushed-stone form; the bitumen is rapidly heated and moved to the laying area in order to be laid.
Bitumen melting devices are also known, which can reduce the viscosity of the bitumen in order to make it malleable and layable in carpets either manually or by means of stand-alone laying machines. Such melting devices comprise a mixing device for increasing the bitumen heating power, thus reducing the risk of excessive heating that might impair the physical characteristics of the bitumen. The bitumen heated by the melting device is normally laid manually for closing microtrenches or holes. Normally such melting devices are designed for providing a volume of bitumen ready for laying of at least 250 liters.
Such melting devices cannot prepare a mixture of bitumen and crushed stone, since they are exclusively dedicated to bitumen preparation only.
It is also known that in the realization of microtrenches, excavations are made 50 cm deep, thus interfering with most underground utilities. The same microtrench is usually 5÷10 cm wide, such width being sometimes excessive for the very small size of the miniducts that need to be laid.
Once the infrastructure has been laid, the trench is partially filled with concrete, e.g. coloured concrete, which requires a few days for consolidating. The trench is then filled level with bituminous material with low bitumen content and small stone elements, commonly referred to as “binder”. This closing is only temporary, in that after a few months the surface will be milled and the final bitumen carpet will be laid. This carpet laid by paver machines is wider than the trench. Therefore, in the processes currently implemented, costly operations are needed which require work to be carried out in the excavation area at least three times, resulting in clear environmental discomfort.
The technique currently in use for making microtrenches has shown some criticalities, such as:                uncontrolled shrinkage of the concrete used for filling, due to its intrinsic poor quality.        wrong belief that the miniducts need to be protected by putting part of the excavation material back into the trench.        
The above criticalities have the following adverse effects on the works carried out:                local crushing of the miniducts in several places, leading to complete obstruction and preventing the laying of the optical cable, thus making it necessary to dig additional holes in order to solve the problem;        lowering of the concrete layer due to shrinking, resulting in a broken road resurfacing carpet and infiltration of water, which can freeze and deteriorate the bituminous surface.        
It is known that microtrenches for laying new infrastructures are excavated along the edge of the road in order to reduce the impact on the road surface and allow vehicles to circulate while the work for digging the microtrench, laying the infrastructure and closing the microtrench is in progress.
As regards the use of concrete, the following considerations must be taken into account:                tensile and shearing stresses are concentrated in a region of the microtrench close to its surface (thickness of less than 0.05 m);        by replacing the first 0.05 m with more ductile and deformable filling material, it is possible to reduce the stress concentrations, resulting in a positive effect on the overall behaviour of the system;        a microtrench filled with concrete alone leads, due to the higher rigidity of this material compared to the road pavement, an increase in the horizontal tensile stresses in the area of contact between the pavement and the microtrench.        
Therefore, the presence of a material having mechanical characteristics similar to those of the carpet and binder layers in the upper part of the microtrench, e.g. 50 mm thick, completely solves the problem caused by concrete use.
It follows that those roads which are more structured, i.e. made as required by the regulations, are less vulnerable.
As previously specified, microtrenches are currently closed with cement or concrete, or with bitumen. The use of cement or concrete provides faster trench closing, but on the other hand it leads to increased degradation of the road surface because of the different thermal expansion and strength of cement compared to bitumen. Since microtrenches are small, the use of bitumen requires manual work because, down to the present day, no machines have been available for laying small bituminous carpets which can also work near the edge of the road.
At present, no machines for preparing and laying a small bituminous carpet exist which can also work near the outer edge of the road surface in a fast and safe manner.